The fuel tank carried by automobiles is used to store hydrocarbon containing fuels such as gasoline or diesel fuel. The tank is a closed structure, and thus, is a structure which may conveniently be made out of polymeric materials, particularly materials which may be blow molded. The precise configuration of a fuel tank is normally quite complex. The designer desires to obtain as large a storage volume of fuel as possible while still having to fit the tank around various other components of the vehicle. Thus, the envelope for the tank may be quite complex in shape.
It is becoming far more common today to create such tanks from plastic materials. These include polyethylene and the like. One of the advantages of moldable, plastic fuel tanks as compared to steel fuel tanks is the ease with which complicated structures may be molded using such procedures as blow molding. Thus, it is becoming far more common to create fuel tanks of polymeric materials rather than steel.
Many vehicles comprise on-board fuel sensing and diagnostic equipment. Typically these systems function by creating a vacuum pressure in the interior of the tank. If there are leaks in any of the tank or any of its associated conduits, the sensor will detect that the vacuum pressure is not being properly resisted by the tank and its related components and will then send a signal to the vehicle operator indicating a malfunction in the fuel system.
It has been observed that one of the problems arising with many polymeric, molded fuel tanks is that some deflection will occur in the fuel tank. As the surfaces of the fuel tank deflect inwardly under the vacuum pressure, this effectively decreases the volume of the tank. As the volume of the tank is thus decreased by the inward deflection of the tank walls, a false "trouble" signal may be generated by the on-board sensing equipment. Thus, in order to be able to continue using the on-board sensing equipment commonly available, it is desirable that the deflection of the fuel tank be limited so as to inhibit substantial change of the volume of the enclosed space.